JP4962837B2 - Infrared sensor manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a bolometer-type uncooled infrared sensor that changes a temperature by absorbing infrared incident light and reads an infrared radiation intensity signal by changing an electric resistance value according to the temperature change.

  A bolometer utilizes the temperature change of the electrical resistance of a metal or semiconductor thin film that is thermally isolated from the substrate material. Generally, when the temperature coefficient of electric resistance (hereinafter referred to as TCR) of the bolometer material is increased, the sensitivity is improved and the temperature resolution (NETD) of the infrared sensor is decreased.

Since an alloy thin film such as a nickel iron alloy has a small TCR of about 0.5% / K, as a bolometer resistor film used for a highly sensitive infrared sensor, a vanadium oxide thin film, a perovskite-type Mn oxide thin film, and YBa _{2 are used.} Conductive oxide thin films such as Cu ₃ O _x thin films are considered advantageous.

  A method of manufacturing an infrared sensor targeting these conductive oxide thin films is described in Patent Document 1, for example.

  In the manufacturing method according to Patent Document 1, a bridge structure formed on a Si substrate via a gap, a bolometer resistance film formed on the bridge structure, and a protective layer formed on the surface of the bridge structure including the bridge film In this case, the organic metal compound is dissolved in a solvent to form a solution, and after coating and drying, a laser beam having a wavelength of 400 nm or less is irradiated to break the carbon-oxygen bond to decompose it into an oxide thin film. ing.

  According to this manufacturing method, in order to obtain a resistance film for a bolometer having a predetermined sheet resistance and resistance temperature coefficient, a laser of about several minutes is required compared with a heat treatment method that requires thermal annealing for several hours to several tens of hours. It has been confirmed that annealing is sufficient.

JP 2002-289931 A

  In the above manufacturing method, although the effect of reducing the number of steps can be obtained by forming the bridge structure, the bolometer resistance film and the protective layer by the coating method, there is a problem that the coating method is not suitable for mass production. .

  In addition, regarding the bolometer resistance film made of vanadium oxide, there is room for improvement in TCR.

  The present invention focuses on the vanadium oxide thin film among the conductive oxide thin films described above, and an object of the present invention is to provide a method for manufacturing an infrared sensor suitable for mass production and capable of improving TCR.

The present invention is a method of manufacturing a bolometer-type infrared sensor that changes a temperature by absorbing infrared incident light and reads a signal of the infrared radiation intensity by changing an electric resistance value according to the temperature change. A step of forming a bridge structure with an insulating material thereon, a step of forming a vanadium oxide thin film on the bridge structure by a dry film forming method, and irradiating the formed vanadium oxide thin film with laser light. alter the material properties, a step shall be the following 1 [Omega · cm for electrical resistivity, and forming a vanadium oxide thin films changes in material properties in a predetermined pattern, vanadium oxide thin film and formed in said predetermined pattern Forming a protective layer made of an insulating material so as to cover the bridge structure.

  In the manufacturing method according to the present invention, any one of a sputtering method, a vacuum deposition method, and a CVD method is used as the dry film forming method.

  In the manufacturing method according to the present invention, the bridge structure and the protective layer are preferably either a SiN thin film or a SiON thin film formed by a CVD method.

  In the manufacturing method according to the present invention, it is desirable to use a laser beam having a wavelength of 157 to 550 nm, preferably a laser beam having a wavelength of 222 to 360 nm, as the laser beam.

In the production method according to the present invention, the irradiation energy of the laser beam is in the range of 10~150mJ / cm ^2, it is desirable that preferably in the range of 30~60mJ / cm ^2.

  In the manufacturing method according to the present invention, it is desirable that the laser light irradiation is performed at a substrate temperature of 350 ° C. or lower, preferably at room temperature.

  In the manufacturing method according to the present invention, it is preferable that the laser beam irradiation is performed in a vacuum or a reducing mixed gas atmosphere.

  According to the present invention, an infrared sensor manufactured by any one of the above manufacturing methods is also provided.

  ADVANTAGE OF THE INVENTION According to this invention, the infrared sensor which is suitable for mass production and can improve TCR can be provided.

  Below, the manufacturing method of the infrared sensor by this invention is demonstrated in detail.

  The present invention relates to a bolometer-type non-cooled infrared sensor that changes a temperature by absorbing infrared incident light, changes an electrical resistance value due to the temperature change, and reads an incident infrared intensity signal.

  Then, after forming a bolometer resistor film on the bridge structure formed on the insulating substrate through the air gap through a dry film forming process, the resistor film is irradiated with laser light under a predetermined condition. It is characterized in that it is formed as a metal oxide film by changing the material characteristics. Here, the change in material characteristics means that the movement of electrons in the metal oxide film is improved by cutting the bond between the metal atoms and oxygen atoms constituting the metal oxide film and separating the oxygen. It means that the resistivity becomes small.

  As the dry film forming step, a vacuum deposition method and a CVD method can be used in addition to the sputtering method.

  A vanadium oxide thin film is used as the bolometer resistor film. Since the vanadium oxide thin film has a film forming temperature as low as 500 ° C. or less, there are few problems in the manufacturing process.

  On the other hand, if the bridge structure and the protective layer are conductive, the sensitivity of detecting the change in electrical resistivity in the bolometer resistor film is lost, so SiN or SiON, which is an insulator with high resistance and high infrared absorption rate An inorganic insulating thin film is used.

  The thickness of the above-mentioned inorganic insulating thin film can be changed between about 0.01-1 micrometer according to the objective.

  An insulating substrate having a vanadium oxide thin film formed on the above bridge structure is set in a vacuum or a chamber in which the atmosphere can be controlled by a reducing gas mixture, and for a predetermined time at a predetermined range of wavelength, light intensity, and repetition frequency. Irradiate with laser light. Then, as already described, the material properties of the vanadium oxide thin film change.

Examples of the reducing gas mixture include H ₂ , NH ₃ , and N ₂ O.

As an ultraviolet laser with a little heating effect for the laser light, an excimer laser such as XeF (351 nm), XeCl (308 nm), KrF (248 nm), ArF (193 nm), F ₂ (157 nm), or an Ar ion laser (second harmonic) : 257 nm) or the like, a laser beam having a wavelength range of 157 to 550 nm can be used. Among these, from the viewpoint of the stability of the laser and the maximum emission energy density, a laser beam having a wavelength range of 222 nm to 360 nm is preferable in that the change in material characteristics can be made uniform.

As for the irradiation energy (density) of the laser beam, irradiation with low energy or high energy is possible by changing the wavelength, and the range of 10 to 150 mJ / cm ² is effective, but 30 to 60 mJ / cm ² is effective. A range of ² is preferred.

  The irradiation frequency of the laser light is 1 to 2000 kHz, preferably 1 to 100 Hz. This is because the pulse frequency of industrial high-power lasers is usually 1 to 100 Hz, but in recent years, high-frequency lasers with low output have been provided, and high-speed processing can be performed as the repetition frequency increases. Because it becomes.

  The pulse width of the laser light is 10 to 200 nsec, preferably 10 to 40 nsec. This is also because the pulse width of a commercially available laser is normally 10 to 40 nsec, but the pulse width can be changed.

  The irradiation time of the laser light is 1 second to 2 hours, preferably 1 second to 30 minutes. This is because the current laser is about 10 to 30 minutes, but in the case of a low-power laser, the irradiation of about 2 hours may be optimal.

  If the laser irradiation energy is too small, the material characteristics do not change, and if it is too large, ablation occurs and the thin film material evaporates.

  In the laser beam irradiation, it is preferable to heat the insulating substrate to a temperature of 350 ° C. or lower, but irradiation at room temperature is also possible.

  Hereinafter, an embodiment of a method for manufacturing an infrared sensor according to the present invention will be described with reference to FIG. 1, but the present invention is not limited to this embodiment.

(Example)
As shown in FIG. 1A, a metal such as WSi, which has high reflectivity in the infrared, is formed on the Si substrate 1 on which the readout circuit is formed by a sputtering method to form an infrared reflection film 8. The prior art is used as it is for the production of the infrared reflecting film 8. Next, photosensitive polyimide is applied on the infrared reflecting film 8 and patterned by lithography, or a polycrystalline silicon film is formed by CVD and patterned to form a sacrificial layer 9 having the shape shown in the figure. .

  Subsequently, as shown in FIG. 1B, an inorganic insulating film made of SiON was formed on the sacrificial layer 9 by plasma CVD. This SiON thin film becomes the bridge structure 2.

Next, referring to FIG. 1C, a metal having a low thermal conductivity, such as Ti, is formed on the bridge structure 2 by sputtering, and the wiring 5 is formed by normal exposure, development, and etching processes. did. Next, after forming the vanadium oxide thin film 4 on the bridge structure 2 by a sputtering method, the entire surface of the thin film was irradiated with a Xecl excimer laser beam 10 having a wavelength of 308 nm at 50 mJ / cm ² , 10 Hz, 5 minutes at room temperature in a vacuum. . Subsequently, a vanadium oxide thin film having a predetermined pattern to be a bolometer resistor 4 ′ (FIG. 1d) was left on the bridge structure 2 corresponding to the infrared reflective film 8 through an exposure, development, and etching process. As a result, the electrical resistivity and TCR of the bolometer resistor 4 ′ irradiated with the laser light changed.

  Next, as shown in FIG. 1D, an inorganic insulating thin film made of SiON was formed on the bridge structure 2 including the bolometer resistor 4 'by plasma CVD. This SiON thin film becomes a protective layer 6 that shields the bolometer resistor 4 from the outside.

  Thereafter, a pattern was formed by exposure and development in a semiconductor, and a slit-like groove (not shown) reaching the sacrificial layer 9 was formed by dry etching with gas. Subsequently, the gap 3 was formed by performing a process of removing the sacrificial layer 9 through the groove of the slit (FIG. 1e).

  A diaphragm having a structure in which the bolometer resistor 4 'is suspended in the air is formed by such a forming method.

  The principle that this cell operates as an infrared sensor is as follows.

  When infrared rays are incident on the cell, the infrared rays are absorbed by the bridge structure 2 and the protective layer 6 having a high infrared absorptance, and part of the infrared rays are transmitted through the structure and then reflected by the infrared reflecting film 8 so that the bridge structure 2 and Absorbed by the protective layer 6. The absorbed infrared rays become heat and heat the diaphragm to change the electric resistance of the bolometer resistor 4 '.

2, the resistive element 4 for the bolometer 'irradiation energy of the laser light provided to the case of ^{40mJ / cm 2, 50mJ / cm} 2, 60mJ / cm 2, an infrared sensor (bolometer resistor 4' of the TCR) It is the characteristic view which measured temperature dependence. In the case of irradiation energy of 50 mJ / cm ² , a good TCR of about 3% / K, which exceeds 2% / K so far, can be obtained around room temperature (300 K).

3, 'the case where the irradiation energy of the laser light irradiated on is ^{40mJ / cm 2, 50mJ / cm} 2, 60mJ / cm 2, an infrared sensor (bolometer resistor 4' for the bolometer resistor 4 resistivity) It is the characteristic view which measured the relationship between irradiation time. At any irradiation energy, when the irradiation time exceeded 2 minutes, the electrical resistivity was 1 Ω · cm or less, and was within the range of electrical resistivity required for the bolometer material.

4, 'the case where the irradiation energy of the laser light irradiated on is ^{40mJ / cm 2, 50mJ / cm} 2, 60mJ / cm 2, an infrared sensor (bolometer resistor 4' for the bolometer resistor 4 resistivity) It is the characteristic view which measured the temperature dependence of.

From the above measurement results, it can be said that a preferable range of irradiation energy in the production method according to the present invention is 30 to 60 mJ / cm ² .

  The infrared sensor according to this example is superior to the infrared sensor disclosed in Patent Document 1 in the following points.

1. TCR can be improved by using SiN or SiON, which has a better infrared absorption rate than SiO ₂ , TiO ₂ , Al ₂ O _3, etc., as the material for the bridge structure and the protective layer.

  2. The vanadium oxide thin film for forming the bolometer resistor is formed not by the coating method but by the sputtering method, and although the coating method reduces the number of steps, the film cannot be uniformly formed on the uneven substrate surface. Not suitable for mass production. On the other hand, the sputtering method has an advantage of being suitable for mass production because a film can be uniformly formed regardless of the unevenness of the substrate.

  3. The substrate temperature is lowered from the conventional 400 to 500 ° C. or lower to 350 ° C. or lower to realize a low temperature.

  It should be noted that the present invention is not limited to the above-described embodiments, and can be appropriately changed within the scope of the technical idea of the present invention.

FIG. 1 is a diagram for explaining one embodiment of a manufacturing process of an infrared sensor according to the present invention. FIG. 2 is a characteristic diagram in which the temperature dependence of the TCR of the bolometer resistor is measured when the irradiation energy of the laser light applied to the bolometer resistor is changed in the manufacturing process of the infrared sensor shown in FIG. is there. FIG. 3 shows the relationship between the resistivity of the bolometer resistor and the irradiation time when the irradiation energy of the laser light applied to the bolometer resistor is changed in the manufacturing process of the infrared sensor shown in FIG. FIG. FIG. 4 is a characteristic diagram in which the temperature dependence of the resistivity of the bolometer resistor is measured when the irradiation energy of the laser light applied to the bolometer resistor is changed in the manufacturing process of the infrared sensor shown in FIG. It is.

Explanation of symbols

1 Si substrate 2 Bridge structure 3 Void 4 Vanadium oxide thin film 4 'Resistor for bolometer 5 Wiring 6 Protective film 8 Infrared reflective film 9 Sacrificial layer 10 Laser light

Claims (7)

In the method of manufacturing a bolometer-type infrared sensor that changes the temperature by absorbing infrared incident light, and reads out the signal of the infrared radiation intensity by changing the electrical resistance value due to the temperature change,
Forming a bridge structure made of an insulating material on an insulating substrate;
Forming a vanadium oxide thin film on the bridge structure by a dry film forming method;
The material properties are changed by the formed vanadium oxide thin film is irradiated with a laser beam, a step shall be the following 1 [Omega · cm for electrical resistivity,
Forming a vanadium oxide thin film having changed material characteristics into a predetermined pattern;
Forming a vanadium oxide thin film formed in a predetermined pattern and a protective layer made of an insulating material so as to cover the bridge structure;
The manufacturing method of the infrared sensor characterized by including.   The method for manufacturing an infrared sensor according to claim 1, wherein the dry film forming method is any one of a sputtering method, a vacuum evaporation method, and a CVD method.   The infrared sensor manufacturing method according to claim 1 or 2, wherein the bridge structure and the protective layer are each a SiN thin film or a SiON thin film formed by a CVD method. The method for manufacturing an infrared sensor according to claim 1, wherein a laser beam having a wavelength of 157 to 550 nm is used as the laser beam . Method for manufacturing an infrared sensor according to claim 1, wherein the irradiation energy of the laser beam, a range of 10~150mJ / cm ^2. Method for manufacturing an infrared sensor according to claim 1, wherein the irradiation of the laser beam, and performing at 350 ° C. hereinafter substrate temperature.   The method of manufacturing an infrared sensor according to claim 1, wherein the laser light irradiation is performed in a vacuum or a reducing gas mixture atmosphere.

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